Several methods are known in the prior art for obtaining blood plasma and/or fractions of whole blood. A classical, well-known approach for obtaining blood plasma or other blood fractions is based on the centrifugation of whole blood samples. The whole blood sample is centrifuged at high speed and, subsequently, the obtained fractions of interest are transferred into new vessels. However, this process requires special laboratory equipment such as centrifuges and furthermore, is difficult to automate.
Other methods for separating red and/or white blood cells from whole blood samples are also known in the prior art.
E.g. U.S. Pat. No. 6,403,384 discloses a gel filtration method in which a cell-free blood plasma fraction is separated from the blood cells by means of capillary flow through the interstitial spacings between densely packed microspheres. U.S. Pat. No. 5,118,428 describes the partial agglutination of erythrocytes induced by the addition of certain acids, subsequently filtering off these erythrocytes by the flow through an appropriate material or removing the erythrocytes by centrifugation or decantation. U.S. Pat. No. 5,876,605 describes the production of blood plasma by means of filtration following the addition of an inorganic salt or amino acid to whole blood. U.S. Pat. No. 5,482,829 discloses the addition of osmotically active agents, i.e. which create a hypertonic solution without entering the cells themselves, and high molecular bridging substances for connecting the red blood cells and thereby enhancing the rate of sedimentation. U.S. Pat. No. 5,609,771 describes the separation of red blood cells from white blood cells by sequentially changing the position of a vessel filled with blood without adding chemicals, in order to permit efficient analysis of the white blood cells. U.S. Pat. No. 5,282,982 shows a blood washing method, in which the addition of substances promoting aggregation causes an accelerated sedimentation rate of the red blood cells and thus a shortened washing period. U.S. Pat. No. 7,754,499 discloses the specific isolation of blood constituents by means of magnetic particles, to which affinity markers such as for example antibodies are coupled, which specifically bind to the blood constituents representing target antigens. Finally, U.S. Pat. No. 3,552,928 describes a whole blood separating means, in which red blood cells are separated from whole blood by flow of the blood through a matrix containing certain amino acids and the resulting colourless fluid is contacted with a test reagent.
As is apparent by the above described prior art methods, the preparation of blood fractions such as blood plasma or white blood cells usually occurs manually and thus cannot be integrated into standard downstream processes that are often, respectively preferably performed on automated systems such as e.g. the isolation of nucleic acids from the obtained blood fractions. Furthermore, some of the respective methods are time consuming, expensive and/or need special equipment such as high speed centrifuges. A particular challenge is to provide a rapid, simple and cost-efficient method for obtaining blood plasma from whole blood that is of a suitable quality to be used in standard downstream applications such as diagnostic assays. Here, it is a particular challenge to provide a method for obtaining blood plasma that has a low risk of destroying red blood cells during the preparation. If the red blood cells are destroyed and accordingly, contaminate the obtained blood plasma, this can cause analytical errors in the downstream processes.
It is the objective of the present invention to provide an alternative method for obtaining blood plasma and/or one or more blood fractions from a whole blood sample. In particular, it was the objective to provide a respective method that is quick, suitable for automation and preferably overcomes one or more drawbacks of the prior art methods.